A semiconductor device that can be used at a constant temperature by being locally heated is described, for example, in Microelectronics Reliability 44 (2004), pages 1251-1262.
FIGS. 4A and 4B show the semiconductor device disclosed in the above prior art, wherein FIG. 4A is a schematic top view of a semiconductor device 90, and FIG. 4B is a schematic cross section view along a line IVB-IVB in FIG. 4A.
In the semiconductor device 90 shown in FIGS. 4A and 4B, a heater 3 formed by a polysilicon film is disposed on a silicon substrate 1 via a thick oxide film 2. The heater 3 as a polysilicon film is applied with current to generate heat, thereby a MOS transistor 9 formed on a surface part of the silicon substrate 1 is locally heated to be able to be used at a constant temperature. In the semiconductor device 90 shown in FIGS. 4A and 4B, a metal resistor 5 formed via a dielectric film 4 is operated as a temperature sensor to control heat generation of the heater 3 (temperature of the MOS transistor 9).
Since the MOS transistor 9 in the semiconductor device 90 is heated by the heater 3 and thus subjected to temperature control, it can be used at a constant temperature. However, the heater 3 formed by the polysilicon film is formed on the thick oxide film 2, causing large heat radiation loss to the outside. Therefore, in the semiconductor device 90 in FIGS. 4A and 4B, even if the heater 3 is operated to generate heat for increasing temperature to 540° C. at the maximum, the MOS transistor 9 formed on the surface-part of the silicon substrate 1 can be heated to at most 250° C. On the other hand, in order to evaluate reliability, high temperature of about 400° C. is necessary for varying characteristics of the MOS transistor 9 formed on the silicon substrate 1 in about several hours in the high-temperature accelerated test. Therefore, a heating structure provided in the semiconductor device 90 in FIGS. 4A and 4B can not provide sufficient temperature necessary for the high-temperature accelerated test and therefore can not be used for evaluation of reliability of the MOS transistor 9.
Furthermore, in the semiconductor device 90 in FIGS. 4A and 4B, the metal resistor 5 as the temperature sensor is formed via the dielectric film 4 formed on the heater 3. Therefore, the MOS transistor 9 formed on the surface part of the silicon substrate 1 is separated from the temperature sensor 5, consequently temperature of the MOS transistor 9 can not be accurately monitored.